A high molecular dispersant for organic, inorganic pigment and heat conductive material special for silicone rubber system and a preparation method thereof

Abstract

The application discloses a special polymer dispersant for organic, inorganic pigment fillers and heat-conducting materials of a silicone rubber system and a preparation method thereof. The dispersant is a polysiloxane with a comb structure, the main chain of which is compatible with a silicone rubber matrix, and the side chain of which is provided with strong anchoring groups such as phosphate ester and phthalimide and long-chain steric hindrance groups. The dispersant is prepared through a silicon-hydrogen addition reaction, can significantly reduce the viscosity of a high-filling silicone rubber system, improve the dispersity of fillers and storage stability, and does not affect vulcanization. The application simplifies the process, improves the mechanics and functionality of a final product, and is suitable for the preparation of silicone rubber composites in the fields of electronics, new energy and the like.

Description

Technical Field

[0001] This invention relates to the fields of organosilicon polymer materials and fine chemical technology, specifically to a functional additive for improving the dispersibility of organic and inorganic pigments, fillers, and thermally conductive materials in a silicone rubber matrix. Particularly, it relates to a polysiloxane-based polymeric dispersant, through specific molecular structure design, which can significantly reduce the viscosity of highly filled silicone rubber systems and improve dispersion stability, and its preparation method. Background Technology

[0002] Silicone rubber (especially addition-cured type) is widely used in electronics, new energy vehicles, medical devices and other fields due to its excellent comprehensive properties. To endow it with specific functions such as thermal conductivity, electrical conductivity, coloring and reinforcement, a large amount of inorganic pigments and fillers are often added, such as alumina, aluminum hydroxide, boron nitride, silicon dioxide, carbon black, titanium dioxide and so on.

[0003] However, inorganic pigments and fillers have high surface energy and are hydrophilic, resulting in extremely poor compatibility with hydrophobic polysiloxane alkyl colloids, leading to the following serious problems: 1. Difficulty in dispersion and high viscosity: Fillers tend to agglomerate in the base adhesive, making it difficult to disperse evenly. To achieve the required filling amount, extremely high shear forces must be applied, and the final paste viscosity increases sharply, resulting in poor flowability and posing significant challenges to processing techniques such as mixing, potting, and coating.

[0004] 2. Poor stability: The dispersed filler is prone to re-aggregation and sedimentation before storage or vulcanization, resulting in uneven product performance.

[0005] 3. Performance loss: Filler agglomerates become stress concentration points and defects, which severely degrade the mechanical properties (such as tensile strength and tear strength) and functional characteristics (such as poor thermal / electrical conductivity) of the cured rubber.

[0006] Currently, the main method to improve filler dispersion is to pretreat the filler surface using silane coupling agents (such as KH-550 and KH-560). While this method has some effect, it has significant limitations: - The process is complicated: it requires multiple steps such as pre-drying, surface treatment and re-drying of the filler, which is a long process and has high energy consumption.

[0007] - Limited and unstable effects: Small molecule silane coupling agents provide little steric hindrance, which limits their viscosity-reducing effect on highly filled systems, and they may become ineffective due to molecular migration during long-term storage.

[0008] - May interfere with curing: Some aminosilanes have an inhibitory effect on platinum catalysts, affecting vulcanization.

[0009] Therefore, the development of a polymeric dispersant that can be directly added to silicone rubber systems, significantly reduces high filler viscosity, provides long-term steric hindrance stability, and does not affect vulcanization is an urgent need in the industry. Summary of the Invention

[0010] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a polymeric dispersant specifically for silicone rubber systems. This dispersant achieves efficient wetting, dispersion, and stabilization of inorganic pigments and fillers in silicone rubber through the chemical combination of "polysiloxane compatible segments" and "strong powder anchoring groups".

[0011] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides an inorganic pigment and filler polymeric dispersant for silicone rubber systems, which is a polysiloxane with a comb-like structure, characterized in that its molecular structure comprises: (A) Polysiloxane backbone: composed of dimethylsiloxane repeating units (D units) and / or methylphenylsiloxane repeating units, ensuring intrinsic compatibility with the silicone rubber matrix; (B) Strong Powder Anchoring Side Chains: These side chains are connected to the silicon atoms of the main chain via flexible connecting chains (such as propyl chains), and their ends are at least one functional group selected from phosphate ester groups (-OPO(OH)2 or its dialkyl esters), phthalimide groups, carboxyl groups (-COOH) and their salts, and polyamine groups (such as ethylenediamine derivatives). These functional groups can undergo strong chemical adsorption or coordination with metal ions, hydroxyl groups, etc. on the surface of inorganic pigments and fillers, achieving firm anchoring.

[0012] (C) Spatially stabilizing segments: located between the anchoring group and the main chain or as another type of side chain, are long-chain alkyl (C12-C22) or polyether segments (such as polyoxyethylene-polyoxypropylene blocks), used to provide a thick solvation layer on the filler surface, generating strong steric hindrance through entropy repulsion effect, preventing filler particles from agglomerating closer together.

[0013] Preferably, the dispersant has the structural unit shown in the following general formula (I): `MD_x D_y D'_z M` in: - M is a trimethylsiloxy-terminated group ((CH3)3SiO-); - D represents a dimethylsiloxane unit (-[(CH3)2SiO]-); - D' is a functionalized siloxane unit (-[(CH3)(R')SiO]-); - R' is a side chain with a "connecting chain-space chain-anchor base" structure, and its general formula is: `-(CH2)3-O-(spacer)-Y`.

[0014] Wherein, `spacer` is a polyoxyethylene chain (EO), a polyoxypropylene chain (PO), or a C12-C18 long-chain alkyl group; `Y` is the strong powder anchoring group.

[0015] - x, y, z represent the degree of polymerization, satisfying a number-average molecular weight (Mn) of 5,000-50,000 and a molar percentage of functionalized unit D' (z / (x+y+z)) of 5%-30%.

[0016] Secondly, the present invention provides a method for preparing the above-mentioned polymeric dispersant, characterized in that a hydrosilylation reaction is used as a key step, specifically including the following route: Route 1: First synthesize the functional monomer, then graft it. 1. Synthesis of functional monomers (FM): Using allyl glycidyl ether as a raw material, it is reacted with phosphoric acid (or long-chain alkanol phosphate) to open the ring and obtain allyl polyether phosphate; or allyl amine is reacted with phthalic anhydride to generate allyl phthalimide.

[0017] 2. Preparation or selection of polysiloxane backbone: Prepare or directly select hydrogen-containing silicone oil with one or both ends capped with dimethoxy groups and side chains containing a certain proportion of methylhydrosiloxane units (HSiO), and control its hydrogen content to be 0.2%-1.0% (wt).

[0018] 3. Hydrosilylation Grafting: The functional monomer (FM) synthesized in step 1 and hydrogen-containing silicone oil are dissolved in anhydrous toluene, and a platinum catalyst (such as Karstedt catalyst) is added. Under nitrogen protection, the reaction is carried out at 80-100℃ for 4-8 hours, and the disappearance of the Si-H bond characteristic peak (~2160 cm⁻¹) is monitored by infrared spectroscopy. After the reaction is complete, the target dispersant is obtained through post-processing.

[0019] Route 2: Post-modification method 1. Preparation of allyl polyether intermediate: Allyl polyoxyethylene polyoxypropylene block ether (APEG) is grafted onto hydrogen-containing silicone oil via hydrosilylation to obtain polysiloxane-polyether copolymer.

[0020] 2. Terminal functionalization: The hydroxyl groups at the ends of the above copolymers are attached with anchoring groups such as phosphate ester groups and carboxyl groups through esterification, amidation or etherification reactions.

[0021] Thirdly, the present invention provides the application of the above-mentioned polymeric dispersant in a silicone rubber composition comprising inorganic pigments and fillers and polyorganosiloxanes. The inorganic pigments and fillers include, but are not limited to: alumina, aluminum nitride, boron nitride, silicon dioxide, carbon black, titanium dioxide, aluminum hydroxide, calcium carbonate, etc.

[0022] Fourthly, the present invention provides a silicone rubber composition comprising: - Polyorganosiloxane raw rubber: 100 parts by weight; - Inorganic pigments and fillers: 10-500 parts by weight (depending on functional requirements); - The above-mentioned polymeric dispersant: 0.5-10 parts by weight (based on the weight of inorganic pigments and fillers); - Crosslinking agents (hydrosilicone oil), catalysts (platinum catalysts) and other additives.

[0023] The beneficial effects of this invention are: 1. Excellent viscosity-reducing effect: Dispersant molecules are rapidly adsorbed onto the filler surface through strong anchoring groups, and form a stable solvation layer around the filler through polysiloxane segments and spatial segments. This greatly weakens the interaction between filler particles, thereby significantly reducing the viscosity of the mixture and improving its flowability. Experiments show that, at the same filler content, adding this dispersant can reduce the viscosity of the system by 30%-70% compared to systems without the dispersant or using only silane coupling agents.

[0024] 2. Excellent dispersion stability: The strong steric hindrance provided by the polymer chains can effectively prevent the filler from re-agglomerating and settling during storage, ensuring the uniformity and stability of the paste.

[0025] 3. Perfect compatibility with silicone rubber: Based on polysiloxane, it has excellent compatibility with silicone rubber matrix, and will not cause phase separation, migration or exudation, and will not affect the transparency (for transparent systems) and surface properties of cured products.

[0026] 4. Improved final product performance: Good dispersion ensures the full functioning of fillers (such as a more complete thermal / electrical network), while reducing stress concentration caused by agglomerates, which helps to maintain or even improve the mechanical properties of vulcanizates.

[0027] 5. Easy to use and simplified process: No complicated pretreatment of fillers is required. They can be added directly during the mixing process, simplifying the production process and reducing energy consumption. Detailed Implementation

[0028] The present invention will be further described below with reference to the embodiments.

[0029] Example 1: Synthesis of Phosphate Ester-Modified Polysiloxane Dispersant (Si-g-PE-P) 1. Synthesis of functional monomers: 100g of allyl polyoxyethylene (10) ether (APEG-400) and 20g of phosphorus pentoxide were reacted at 80℃ for 5 hours to generate allyl polyether phosphate (FM-P).

[0030] 2. Take 50g of hydrogen-containing silicone oil (HSi% = 0.5%, Mn≈8000) and dissolve it with 30g of FM-P obtained in the previous step in 150g of toluene.

[0031] 3. Add an appropriate amount of Karstedt platinum catalyst, heat to 90°C under N2 protection, and react for 6 hours until the Si-H peaks in the IR display basically disappear.

[0032] 4. Remove the solvent by vacuum distillation to obtain a pale yellow viscous liquid product A.

[0033] Example 2: Synthesis of Phthalimide-Modified Dispersant (Si-g-PI) 1. Synthesis of functional monomer: N-allyl phthalimide (FM-PI) was prepared by refluxing allylamine with phthalic anhydride in toluene.

[0034] 2. Using a hydrosilylation step similar to that in Example 1, FM-PI was grafted onto hydrogen-containing silicone oil to obtain product B.

[0035] Application test case: Base adhesive: Vinyl-terminated polydimethylsiloxane (100 parts).

[0036] Filler: Aluminum hydroxide (ATH, 150 parts).

[0037] Comparative systems: 1# blank (no dispersant); 2# with 1.5 parts (based on ATH) KH-550 silane coupling agent; 3# with 1.5 parts of product A of this invention; 4# with 1.5 parts of product B of this invention.

[0038] After mixing, the viscosity of the paste was tested (25°C, Brookfield rotor, 20 rpm) and the viscosity change rate after 7 days of storage.

[0039] system Initial viscosity (Pa·s) Initial viscosity (Pa·s) viscosity change rate after 7 days blank 850 benchmark +15% (thickens) KH-550 620 -27% +8% Product A 350 -59% +2% Product B 400 -53% +3% Conclusion: Compared with traditional small molecule silane coupling agents, the polymeric dispersant of this invention has a more significant viscosity-reducing effect and can provide better storage stability.

Claims

1. An inorganic pigment and filler polymeric dispersant for silicone rubber systems, comprising a modified polysiloxane with a comb-like structure, characterized in that... The main chain of the polysiloxane has multiple side chains connected by silicon atoms, and the ends of the side chains contain at least one strong powder anchoring functional group selected from phosphate ester group, phthalimide group, carboxyl group and its salt, and polyamine group.

2. The dispersant according to claim 1, characterized in that, The side chain has the general formula: `-(CH2)3-O-(spacer)-Y`, where spacer is a polyoxyethylene chain, a polyoxypropylene chain, or a C12-C18 alkyl chain; and Y is the strong powder anchoring functional group.

3. The dispersant according to claim 1 or 2, characterized in that, The polysiloxane has a number average molecular weight of 5,000-50,000.

4. A method for preparing the dispersant as described in any one of claims 1-3, characterized in that, include: Strong powder anchoring functional monomers with alkenyl groups at the end or in the side chain are subjected to hydrosilylation reaction with hydrogen-containing polysiloxanes in the presence of a platinum catalyst.

5. The method according to claim 4, characterized in that, The strong powder anchoring functional monomer is allyl polyether phosphate or N-allyl phthalimide.

6. The use of the polymeric dispersant as described in any one of claims 1-3 in improving the dispersibility of inorganic pigments and fillers in silicone rubber compositions.

7. A silicone rubber composition, characterized in that, It comprises polyorganosiloxane raw rubber, inorganic pigments and fillers, and the polymeric dispersant as described in any one of claims 1-3.

8. The silicone rubber composition according to claim 7, characterized in that, Based on the weight of the inorganic pigments and fillers, the amount of polymeric dispersant added is 0.5%-10%.

9. The silicone rubber composition according to claim 7 or 8, characterized in that, The inorganic pigments and fillers are alumina, aluminum hydroxide, carbon black, or silicon dioxide.